The present invention relates to wireless power transfer, and more particularly to bidirectional power transfer to and from a remote device.
There has been an ever increasing presence of remote devices in public use. Remote devices such as mobile phones, digital music players, tablets, personal digital assistants, sensors and other similar electronic devices have become nearly ubiquitous in many parts of the world.
As the presence of these types of remote devices increases, their design and feature set changes and advances from one product cycle to the next. In particular, the power interface for charging or powering remote devices has advanced in many respects. Several early remote devices were designed to receive power from a power supply, such as a an AC adapter, via a cord and connector interface. However, these conventional connector interfaces suffer from a variety of drawbacks. The connector interface in some instances is a proprietary interface, which can become a barrier to interoperability with other remote devices. Connector interfaces also may leave electrical contacts exposed so that environmental factors, such as exposure to water, can damage the remote device. And, these interfaces are often prone to mechanical failure.
To address these issues, wireless power interfaces have been utilized more recently to remove the cord and connector interface. Wireless power interfaces may take advantage of coupling between a primary (also known as a transmitter, a primary coil, or a primary inductor) and a secondary (also known as a receiver, a secondary coil, or a secondary inductor) in order to transfer power from a power supply to a remote device without electrical contacts or without a cord and connector interface. For example, wireless power transfer to a remote device may be achieved by energizing a primary such that it inductively couples with a secondary incorporated in the remote device.
With the proliferation of remote devices capable of receiving wireless power, it has been recognized by some that remote devices may be capable of transmitting wireless power in addition to receiving wireless power. Practically speaking, there are some similarities between conventional wireless power supplies and remote devices that make such bidirectional power transfer possible. Both, for example, include a coil in many configurations, which can be used as both a secondary and a primary. However, there are some differences: conventional wireless power supplies include drive circuitry to energize the primary whereas conventional remote devices include passive rectification circuitry to condition power received in the secondary.
To complement the increase in remote devices capable of receiving wireless power, wireless power supplies, such as charging bases, have become more commonplace. Unlike cord and connector interfaces, which use wall power, conventional wireless power supplies often remain idle while awaiting a remote device to power. While idle, the power supply may draw constant power from its power source. This constant draw, though small, may amount to a large waste of energy over long periods or when compounded by multiple power supplies being left idle. There have been solutions to minimize this waste, but none appear to substantially or completely eliminate this waste. For example, some systems have been developed to include supervisors that shut down the power supply for a period of time, but in these systems some circuitry remains on and still draws power, including for example the supervisor and converter circuitry.